X-ray Microanalysis

Comparison of the two x-ray techniques is shown in Table 2.2. Microanalysis in the SEM is best conducted by a combination of these two techniques to take advantage of the strengths of both. Several spectrometers can be mounted on the microscope. Computer hardware and software are available which control both types of spectrometer and combine the data on a single system. Microanalysis in the TEM and STEM is conducted by EDS analysis and EELS. 

There are three major problems with microanalysis of thin films in the AEM  

Polymer specimens are particularly difficult to analyze in the AEM. Generally, there are small amounts of heavy elements in a polymer. These low levels are difficult to detect in a material that changes readily in the electron beam. These difficulties preclude routine quantitative analysis of polymers in either the SEM or AEM although microanalysis techniques can be applied. The major consideration for the polymer microscopist is that changes occur in the polymer during study. 

When a high energy electron beam impinges upon a specimen, x-ray photons are produced. They fall into two classes. Characteristic x-rays have well defined energies that are characteristic of the atoms in the specimen. These x-rays 

Two different types of detectors are used to measure the x-ray intensity as a function of wavelength or energy. In an energy dispersive x-ray spectrometer (EDS), x-rays generated from the sample enter a solid state silicon detector (a reversed bias p-n junction). They 

Interfaced with SEM, TEM, STEM Interfaced with SEM, EPMA 

Simultaneous detection of elements Quantitative detection of one element at a time 

The backscattered electron image is produced from signals coming from almost the same excitation volume as the x-ray signal (Fig. 2.3). This is helpful, as BEI can be used to scan the specimen quickly for atomic number differences to guide the slower x-ray mapping. 

In a wavelength dispersive x-ray spectrometer (WDS) the x-rays fall on a bent crystal and are reflected only if they satisfy Bragg s law. The crystal is set to focus x-rays of one specific wavelength onto a detector and rotates to scan the wavelength detected. Only one element can be detected at a time with one crystal. The resulting WDS spectra are quite sharp and elemental overlap is minimal due to the good signal to noise ratio. 

In WDS, or in the EPMA, quantitative analysis is possible if the specimen is flat and standards are used for calibration. Computer software is available to permit reliable analyses. It takes into account such critical complicating features as atomic number, x-ray absorption and fluorescence, which depend on the path length and depth in the specimen. These techniques are used with polymeric materials, but normally to 

Mathey and Hoder (5J0) have applied the technique of cathodoluminescence and X-ray microanalysis to the identification of vinetorin, 3-0-methyl-2,5,7-trichloronorlichexanthone and of quinones in some crustose lichens. 

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R. E. Lee, Scanning Electron Microscopy and X-Ray Microanalysis, PTR Prentice Hall, Englewood Cliffs, NJ, 1993. 

METHODICAL TECHNIQUES FOR RESEARCH OF RARE-METAL AND RARE-EARTH MINERALS WITH X-RAY MICROANALYSIS... 

The X-ray microanalysis is the basic method of study of rare-metal and rare-earth minerals of micron size. The multi-component composition, instability of minerals under the electron beam, overlap of X-ray characteristic lines, absence of reference samples of adequate composition present difficulties in the research of mineral composition. 

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

J. I. Goldstein, Dale E. Newbury, P. Echlin, D. C. Joy, C. Fiori, and E. Lif-shin. Scanning Microscopy and X-Ray Microanalysis. Plenum Press, New York, 1981. An excellent and widely ranging introductory textbook on scanning microscopy and related techniques. Some biological applications are also discussed. 

Future developments of this instrumentation include field emission electron sources at 200-300 kV that will allow better elemental detectability and better spatial resolution. Multiple X-ray detectors having large collection angles will also improve elemental detectability in X-ray microanalysis. The higher accelerating... 

High Resolution Transmission Electron Microscopy and Associated Techniques. (P. R. Buseck, J. M. Cowley, and L. Eyring, eds.) Oxford University Press, New York, 1988. A review covering these techniques in detail (except X-ray microanalysis) including extensive material on high-resolution TEM. 

Electron Probe X-Ray Microanalysis (EPMA) is a spatially resolved, quantitative elemental analysis technique based on the generation of characteristic X rays by a focused beam of energetic electrons. EPMA is used to measure the concentrations of elements (beryllium to the actinides) at levels as low as 100 parts per million (ppm) and to determine lateral distributions by mapping. The modern EPMA instrument consists of several key components ... 

K. F. J. Heinrich, Electron Beam X-Ray Microanalysis,Vzn Nostrand, New York, 1981. 

Melford, D.A. (I960) Proceedings of Second International Symposium on X-ray Microscopy and X-ray Microanalysis, Stockholm (Elsevier, Amsterdam) p. 407. 

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Selective removal of the less noble constituent has been demonstrated by chemical analysis in the case of nickel-rich alloys in fused caustic soda or fused fluorides ", and by etching effects and X-ray microanalysis for Fe-18Cr-8Ni steels in fused alkali chlorides. This type of excessive damage can occur with quite small total amounts of corrosion, and in this sense its effect on the mechanical properties of the alloy is comparable with the notorious effect of intercrystalline disintegration in the stainless steels. 

Goldstein JI, Newbury DE, Ecklin P, Joy DG, Fiori G, Lipshin E (1981) Scanning electron microscopy and X-ray microanalysis, Plenum, New York... 

Subsequent investigation into what features might distinguish the femur from Burial 8 initially foeused on the mineral fraction of a selection of Snake Hill femora. Energy dispersive x-ray microanalysis (JEOL JSM-35C SEM equipped with a TN-5500 X-ray analyzer) demonstrated consistent calcium to... 

Storey, R., Pitman, M.G., Stelzer, R. Carter, C. (1983). X-ray microanalysis of cells and cell compartments of Atriplex spongiosa. I. Leaves. Journal of Experimental Botany, 34, 778-94. 

I. Bondarenko, H. Van Malderen, B. Treiger, P. Van Espen and R. Van Grieken, Hierarchical cluster analysis with stopping rules built on Akaike s information criterion for aerosol particle classification based on electron probe X-ray microanalysis. Chemom. Intell. Lab. Syst., 22 (1994) 87-95. 

W. Van Borm, Source Apportionment of Atmospheric Particles by Electron Probe X-ray Microanalysis and Receptor Models. Doctoral Thesis, University of Antwerp, 1989. 

The analytical electron microscope (AEM) is fitted with a spectrometer for X-ray microanalysis and also for electron energy-loss analysis (q.v. pp. 185). 

All quantitative X-ray microanalysis requires that the background Bremsstrahlung be subtracted from the observed spectrum, so that the relative intensities of the characteristic X-rays can be determined. 

Cliff and Lorimer (1975) used this equation to form the basis for X-ray microanalysis of thin foils, where the constant kAB contains all the factors needed to correct for atomic number differences. kAB varies with operating voltage, but is independent of sample thickness and composition if the two intensities are measured simultaneously. Its value can be determined experimentally with accuracy, using specimens of known composition. The value of kAB can be determined by calculation more rapidly, but with less accuracy. 

Composition Profile Measurement. Results of Zieba et al. (1997) will be given as an example of the measurement of solute distribution in an alloy undergoing a phase transformation. They studied discontinuous precipitation in cobalt-tungsten alloys, in which a Co-32 wt% W alloy was aged in the temperature range 875 K to 1025 K, and high spatial resolution X-ray microanalysis of thin foils by STEM was used to measure the solute distribution near the reaction front. 

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